Hydraulic motor

ABSTRACT

A hydraulic motor of the type having reciprocating pistons within cylinders and having two separate valve devices. The first times the strokes of the pistons, the second determines whether the cylinders are connected to pressure or exhaust and if so which. The first valve device is situated between pressure/exhaust and the second valve device. Preferably the motor is of the rotary type, the cylinders and pistons being carried on the output member.

United States Patent Applv No. Filed Patented Assignee Priority HYDRAULIC MOTOR Claims, 12 Drawing Figs.

US. Cl 91/35, 91/l76,91/l80, 91/375, 91/376, 91/390, 91/498 Int. Cl F0lb 1/06, F01b13/06, Fb 13/16 [50] Field of Search 9l/375, 205, 461, 376,176,

[56] References Cited UNITED STATES PATENTS 2,823,619 2/1958 Nlay 91/205 2,964,014 12/1960 Quintard 9l/375 3,131,602 5/1964 Ford 91/375 3,185,439 5/1965 lnaba et a1. 91/375 Primary Examiner-Paul E. Maslousky Attorney-Cushman, Darby & Cushman I 1 I a 'Z 8 II 19 M 2/ 255; 36 V n" 34 3 k J I 45 32 3a, 4247 4,? 553/ 47 C Y -2 -52 -2/ K 5/ 7 1 am 4 72257 E SHEET 1 [IF 8 mNE k PATENTEB JUN 8197! PATENTED JUN 8 I97! SHEET 2 BF 8 PATENTEU JUN 81971 SHEET '4 OF 8 HYDRAULIC MOTOR The present invention relates to servomotors.

According to the present invention there is provided a servomotor comprising an input shaft, an output shaft, a stationary member, an inlet and outlet for hydraulic fluid, a motor operable to move the output shaft relative to the stationary member, said motor comprising a plurality of pistons located one in each of a like plurality of cylinders, the pistons cooperating with a cam surface whereby when the working spaces within the cylinders behind the pistons are pressurized and exhausted in appropriate sequence the output shaft is moved relative to the stationary member the motor being characterized by a ported device a first part of which is fixed with respect to the stationary member, a second part of which is fixed with respect to the input shaft and a third part of which is fixed with respect to the output shaft, the ported device serving to control hydraulic fluid flow between the inlet and outlet and the working spaces, the arrangement being such that when the position of the output shaft corresponds to the position of the input shaft communication between the inlet and outlet and the working spaces is prevented by the ported device, and that displacement of the input shaft and said second part of the ported device relative to the stationary member causes communication between the working spaces and the inlet and outlet to be so created that the output shaft and with it the third part of the ported device is moved by the motor to a position corresponding to the new position of the input shaft at which position communication between the working spaces and the inlet and outlet is prevented by the ported device, and that displacement of the output shaft and with it the third part of the ported device relative to the stationary member and the input shaft causes communication between the working spaces and the inlet and outlet to be so created that the output shaft is returned by the motor to a position corresponding to that of the input shaft and when so returned communication between the working spaces and the inlet and outlet is prevented by the ported device.

The pistons may, for example, be in the form of balls.

The servo motor may be either rotary or linear acting.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. I is a view in axial section of a first embodiment of the invention;

FIG. 2 is a sectional view taken on the line "-1! in FIG. 1;

FIG. 3 is a sectional view taken on the line III-III in FIG. 1;

FIG. 4 is a sectional view taken on the line IV-IV in FIG. 1;

FIG. 5 is a cross section taken on the line V-V in FIG. I;

FIG. 6 is a sectional view taken on the line VI-VI in FIG. 1;

FIG. 7 is a diagrammatic representation of a development of circular, ported components in the embodiment illustrated in FIG. 1;

FIG. 8 is similar to the portion of FIG. 7 between the lines A and B, with some of the components in different operative positions;

FIG. 9 is similar to FIG. 8 with components again in different operative positions;

FIG. 10 is a view in axial section of a second embodiment of the present invention;

FIG. 11 is a view on the line XI-XI in FIG. 10; and

FIG. 12 is a diagrammatic development of circular, ported components included in the embodiment illustrated in FIG. 10.

In FIG. 1 there is illustrated a servomotor comprising first, second, third, fourth and fifth housing parts, I, 2, 3, 4, 5.

The first and fifth housing parts I, 5 are of annular form and have formed therein annular channels 6, 7, 8, 9 (see FIG. 2) in opposed radial surfaces 10, 11. The second and fourth housing parts 2, 4 have radial surfaces 12, 13, which abut against the surfaces 10, 11 respectively, and axially directed cylindrical extensions l4, 15 which engage at their free ends the third housing part 3 which is of annular form and has formed on its radially inner surface I6 a cam track of a ball motor to be described.

The five housing parts 1 to 5 are rigidly secured together by means, including bolts 17, whereby the housing parts form a rigid, unitary housing.

Each of the housing parts I and 5 has formed therein two passages 18 (only one being shown) leading one to each of the two annular channels 6, 7 or 8, 9, one from each of four hydraulic supply and return conduits 19 (two being shown) at the exterior of the motor.

The fifth housing part 5 has a flange 20 for connection of the motor to a device to be controlled by the motor.

Each of the first and fifth housing parts 1 and 5 has formed in its surface 10 or 11, respectively, three annular grooves 21 in which are located 0 ring seals 21' which prevent leakage of hydraulic fluid from the annular channels 6, 7, 8, 9.

The second, third and fourth housing parts 2, 3, 4 bound a chamber 22 in which are located rotary elements of the motor and from which there is a drainway (not shown).

Secured to an axially directed annular extension 23 of the second housing part 2, which extension 23 is located within a central aperture 24 of the first housing part 1, is a tubular mounting flange 25 of an electrical stepping motor 26 which has an output shaft 27 connected at 28 to an input shaft 29 of the servomotor according to the present invention. The input shaft 29 extends through a central bore 30 in the second housing part 2 and its end 31 is located at approximately the middle of the axial length of the servomotor within the chamber 22. A seal 32 seated in a counter bore in the second housing part 2 cooperates with the surface of the input shaft 29 to prevent escape of hydraulic fluid outwardly along the central bore 30.

An output shaft 33 extends outwardly of the chamber 22 through a central aperture 34 in the fourth housing part 4. The output shaft 33 is journaled in the fourth housing part 4 by a roller bearing 35 and a seal 36 is provided to prevent egress of hydraulic fluid along the output shaft 33.

Integral with the output shaft 33 is a radially directed flange 37 which, at its radially outer periphery, is integral with an annular cylinder block 38 which, in the present embodiment, has formed therein 16 cylinders 39 the axes of which are radial to the aligned axes of the input and output shafts 29, 33 and are uniformly angularly disposed about the axis of the output shaft 33 (see FIG. 6). Each cylinder 39 is open at the radially outer periphery of the block 38 and faces the cam track 16 of the third housing part 3. A bore 40, coaxial with the cylinder 39, extends from the radially inner end of each cylinder 39 to the radially inner cylindrical surface of the cylinder block 38. A ball 41 is located as a sliding fit within each cylinder 39.

Secured to the end of the cylinder block 38 remote from the flange 37 is an annular member 42 which, at its radially inner periphery, mounts a bearing 43 which serves to journal the input shaft 29. A seal 44 is provided to prevent flow of hydraulic fluid between the mutually engaging surfaces of the block 38 and the annular member 42.

Roller bearings 45 are provided to prevent axially directed movement of the rotor, formed by the shaft 33, flange 37, block 38 and annular member 42, relative to the housing formed by the five parts 1 to 5.

Integral with the end 31 of the input shaft 29 is a disc member 46 which, at its cylindrical, radially outer periphery, is a fit within the radially inner surface of the cylinder block 38 although there is freedom of relative rotational movement between the cylinder block 38 and the disc member 46. The radial surfaces of the disc member engage radial surfaces of the annular member 42 and the flange 37, respectively, in such a manner that there can be relative rotational movement between the members. Central regions 47 of the disc member are recessed and bores 48 provide access between the recesses 47.

Control of hydraulic fluid flow between the conduits 19 and the working space behind the balls 41 within the cylinders is provided by a ported device a first part of which is formed by the second and fourth housing parts 2, 4. Reference is now made to FIG. 3 which is a cross section of the fourth housing part 4. The housing part 4 has formed therein eight radially directed passages 48' which are stopped by plugs 49 at their radially outer extremities Each radially directed passage 48' is in communication with two axially directed passages. One, 50, of the axially directed passages in communication with each radially directed passage 48' is located at the radially inner end of the radially directed passage 48' and the eight passages 50 are located on a circle coaxial with the aligned axes of the input and output shafts 29, 33 and extend towards the disc member 46 and terminate in arcuate ports 50 (FIG. 4) in the radial surface facing the disc member. The other axial passage extends towards the fifth housing part 5. The other passages are located alternately on two different radii, four of the axial passages 51 being located on a radius equal to that of the annular channel 8 and the other four axial passages 52 being located on a radius equal to that of the annular channel 9. Thus, successive passages 50 are in continuous communication with the channels 8, 9 alternately when considered proceeding around the circle on which the passages 50 are located.

The annular channel 8 is in communication with a first of the passages 18 by an axial passage 53 and the annular channel 9 is in communication with a second of the passages 18 by an axial passage. Similarly, the channels 6 and 7 are in communication with passages 18 (not shown) and hence conduits 19 by axially directed passages 55,54, respectively (see lFlG. 2).

It is to be understood that the second housing part 2 includes axially directed and radially directed passages and arcuate ports of the form described in relation to the fourth housing part 4. However, the passages and ports in the second housing part are angularly offset from the passages in the fourth housing part 4 by an amount to be described.

Reference is now made to FIG. 5. The flange 37 integral with the output shaft 33, and the annular member 42, each has formed therein sixteen axially directed passages 56 which are uniformly, angularly disposed about the axis of the input and output shafts, the passages 56 in the member 42 being offset from the passages 56 in the flange 37 by an amount to be described. The passages 56 are located on circles of the same radius as the circles on which the passage 50 and ports 50 are located. The passages 56 are open at both radial surfaces of each of the flange 37 and member 42.

Reference is now made to FIGS. 1 and 6. The disc member 46 includes 16 axially directed passages 57 uniformly, angularly disposed on a circle having its axis aligned with the common axis of the input and output shafts 29, 33 and of a diameter equal to circles on which lie the passages 56, 50 and ports 50. The passages 57 are open at both the radial surfaces of the disc member 46. The disc member is also provided with I6 radially directed passages 58 leading one from each of the axial passages 57 to a port 58 in the radial surface of the disc member 46. The plane in which lie the axes of the passages 58 is the same as the plane in which lie the axes of the passages 40 leading from the bottoms of the cylinders 39 to the radially inner surface of the cylinder block 38.

Reference is now made to FIG. 7 which is a diagrammatic representation ofa development of the ported device comprising the housing, the flange 37, annular member 42 and disc member 46.

As can be understood from FIG. 7, the passages 56 in the flange 37 are angularly offset from the passages 56 in the annular member 42 by an angle equivalent to the angle subtended at the axis of the motor by one passage 57 in the disc member 46, that is, there is an edge to edge valving arrangement.

The passages and the centers of the arcuate lengths of the ports in the second housing part 2 are angularly offset from the similar elements in the fourth housing part which control the ball operation in the sector described by the same half lobe of the cam, by an angle corresponding to the sum ofthe angles subtended at the axis by one passage 56 and one passage 57.

The sum of the angles subtended at the axis by one passage 56 and one port 50' is equivalent to the angle subtended at the axis by half a lobe of the cam track l6 but if the angle subtended by one port 50 is reduced so that the aforesaid sum is somewhat less than the angle subtended by half a lobe, a cam track having dwells may be used, which allows greater tolerance in the dimensioning of the parting arrangement, that is, of the ports 50' with respect to the passages 56.

Purely by way of example, it may be mentioned that, in one form of the present embodiment:

a. the angle subtended by one passage 56 is 7 6 b. the angle subtended by one passage 57 is 79? If the angle subtended by one passage 57 is increased or decreased with respect to the dimensions quoted which provide edge to edge valving, then respective underlay and overlap valving is achieved. Underlay valving is advantageous for the transient functioning of the motor due to its damping influence.

Amongst the factors affecting the selection of the sizes of the passages 56 and 57 are:

I. the desire to provide for adequate flow of working fluid without considerable pressure drop, in order to achieve a high rotational speed;

2. the fraction which the angle subtended by one passage 57 represents in relation to the angle subtended by half a cam lobe. In the form of the embodiment, dimensions of which have been described above, this fraction is one sixth. It is this relationship which limits the acceptable lag of the output shaft behind the input shaft. In the above described form of the present embodiment the acceptable lag is 7 ff.

FIG. 7 represents the situation when the output shaft 33 is in a position which corresponds to the position of the input shaft 29 and the cylinder block 38 is hydraulically balanced in this position because both ends of each passage 57 are closed by the radial surfaces of the flange 37 and annular member 42.

In the particular condition illustrated in FIG. 7 four balls 41 B, F, .l, N are on bottom dead center of their strokes and four balls 41 D, H, L, Q are on top dead center of their strokes.

If a signal is sent to the electrical stepping motor 26 which causes it to rotate its shaft 27 and consequently the input shaft 29 and disc member 46 through a small angular extent to a new position, the following procedure occurs.

Reference is now made to FIG. 8 which illustrates the condition when the input shaft is leading the output shaft. In FIG. 8, the disc member 46 has moved slightly to the left from its position relative to the other members. Let it be assumed that leftwards movement of members in FIGS. 7, 8, 9 corresponds to a clockwise motion of the members as viewed along the axis of the shafts from left to right in FIG. I.

It will be seen that the displacement of the disc member 46 has opened the passages 57 to the passages 56 in the flange but has not opened the passages 57 to the passages 56in the annular member 42. At this time only alternate passages 56 in the flange 37 are open to the arcuate ports 50 and those passages 56 which are open to arcuate ports 50' are open to successive ports 50' which, as explained above, are in continuous communication with the annular channels 8, 9 alternately. The channel 8 is supplied with pressure fluid and the channel 9 is connected to a return at return or tank pressure. Therefore, pressure fluid flows from channel 8 through passage 51, passage 50, port 50 to passage 57E from which it flows through passages 58 and 40 to the working space behind the ball 41E in its cylinder 39. The presence of hydraulic fluid under pressure in the working space tends to cause the ball 41E to move radially outwards and, by reaction with the cam surface 16 of the housing, the cylinder block 38 and with it the member 42, flange 37 and output shaft 33 are caused to rotate clockwise which is a leftwards movement of these members as illustrated in FIG. 8. Upon movement of the cylinder block 38, by reaction with the cam surface 16, the ball 416 is driven radially inwards thereby forcing fluid out of its associated working space through passages 40, 58, 57G, 56, port 50', passages 50, 52 to the annular channel 9 to the associated outlet conduit 19. As the member 42 and flange 37 move leftwards in unison, as considered in FIG. 8, communication of the passages 57 with the channels 8, 9 is progressively closed until, when the output shaft is in a position corresponding to the input shaft the passages 57 are closed.

While this is happening passages 56, which are in communication through passages 50 and ports 50' with channels 6 and 7, are blocked at all times, since they register with the solid parts of the face of member 46 lying between adjacent passages 57. Whilst the operation of only two balls, balls 41E and 41G has been considered, it will be realized that the operation of the balls 41A, l, and M is similar to that of the ball 41E and the operation of balls 41C, K, P is similar to that of the ball 41G. As can be seen in FIG. 7, the balls 418, F, ,I, N are at bottom dead center and pressure fluid will flow into their working spaces as the flange 37 moves leftwards (FIG. 8) and communication of passages 578, F, .I, N, with respective ones of the ports 50' in communication with channel 8, containing pressure fluid, is created through the appropriate passage 56. The balls 41D, H, L, Q are at top dead center and fluid will flow out of their working spaces as the flange 37 moves leftwards (FIG. 8) and communication of passages 57D, H, L, Q with respective ones of ports 50' in communication with channel 9 which contains return, low pressure fluid, is created through the appropriate passage 56 by opening of the passage 56 to the port 50'. However, flow to or from the passages 573, F, .I, N and D, H, L, Q is also prevented, by closing of the passages 56, when the output shaft is in a position corresponding to that of the input shaft.

If the input shaft 29 is rotated in a counterclockwise direction as viewed along the axis of the input and output shafts in the direction from left to right in FIG. 1, this rotational direction corresponding to a rightwards movement of the disc member 46 in FIGS. 7 and 8, the passages 57A to 0 remain closed by the flange 37 but become open to the passages 56 in the annular member 42. Thus, rather than become open for communication with the channels 8, 9, the passages 57A to 0 become open to the channels 6 and 7. The channel 6 is continuously supplied with hydraulic fluid under pressure and the channel 7 is at all times a return channel in which the hydraulic fluid is at nominally zero pressure. A consideration of the portion of FIG. 7 between the lines A and B will show that the output shaft is driven in a counterclockwise direction to a position corresponding to that imposed upon the input shaft.

The passage 57D becomes open to a passage 56 which is closed by the second housing part, the ball 41D being at top dead center at this time. The passage 57E becomes open through a passage 56 in the annular member 42 to a port 50' in communication with the return channel 7 and hence the ball 415 can move inwards. The passage 57F becomes open to a passage 56 which is closed, the ball 41F being at bottom dead center at this time. The passage 57G becomes open to a passage 56 which is open to a port 50' in the second housing part 2 which is in communication with the supply channel 6 and hence the ball 416 is forced outwards and, by reaction of the ball with the cam surface 16, the cylinder block 38, flange 37 and output shaft 33 are moved rightwardly as seen in FIG. 7 which corresponds to the aforementioned counterclockwise rotational direction. As soon as some movement of the output shaft has occurred in the counterclockwise direction from the particular condition illustrated in FIG. 7, the passage 57D comes into communication with the return channel 7 and hence the ball 41D can move inwardly. Similarly, the passage 57F comes into communication with the supply channel 6 and the ball 41F is forced radially outwards. When the output shaft arrives at a position corresponding to that of the input shaft, all the passages 57A to Q are closed at both ends and the cylinder block 38 and output shaft 33 are hydraulically locked in that position.

If there should be some departure of the output shaft 33 from its position corresponding to that of the input shaft, due, for example, to leakage of hydraulic fluid over a period of time resulting in the loss of the hydraulic balance or to torque loading of the output shaft, then a condition is created which returns the output shaft to its required position. Such a condition is illustrated in FIG. 9 which illustrates a condition when the output shaft 33 has rotated through a small angle in the aforementionedcounterclockwise direction (i.e. rightwards in FIGS. 7 and 9) relative to the input shaft 29.

Counterclockwise rotational displacement of the output shaft 33 causes a rightwards displacement of the balls 41, annular member 42 and flange 37 as illustrated in FIG. 9. As can be seen in FIG. 7, whilst such rightwards displacement has opened some of the passages 56 in the annular member 42 to the ports 50 in the second housing part 2, which were previously closed, and thereby reduced all of these passages 56 open to the ports 50 in the second housing part 2, none of the passages 56 in the annular member 42 become open to the passages 57. However, rightwards movement (in FIG. 9) of the flange 37 opens each of the passages 57 to a respective one of the passages 56 in the flange 37. In the particular angular relationship of the cylinder block to the cam surface 16 which is committant with the condition illustrated in FIG. 9, all of the passages 56 in the flange 37 are open to respective ports 50'. The passage 57E is in communication with the supply channel 8 and therefore pressure fluid flows into the working space behind ball 41B and forces the ball 41E outwards thereby tending to rotate the cylinder block 38 clockwise, that is, move the annular member 42 and flange 37 leftwards as seen in FIG. 8. The passage 57F is in communication with the return channel 9 and therefore ball 41F can move inwards as can ball 41G because the passage 576 is also in communication with the return channel 9. Though it is not readily apparent in FIG. 9, the passage 57D is in communication with the supply channel 8 and therefore the ball 41D is forced radially outwards. The output shaft 33, therefore, rotates in a clockwise direction until it returns to a position corresponding to that of the input shaft and when in such a position is locked in that position by closing of the passages 57 by the annular member 42 and the flange 37. It will be realized that an oppositely directed returning torque is created if the output shaft is displaced clockwise, i.e. leftwards with regard to FIG. 9. However, the supply and return of hydraulic fluid would occur through channels 6 and 7 respectively rather than channels 8 and 9.

Whilst the operation of only four balls 41 has been considered it will be understood that in the present embodiment which is a sixteen ball four lobe arrangement, the operation of any four successive balls may be derived from the particular set of four balls chosen for description.

Whilst only small relative displacements of the several members and parts has been described above, it will be understood that larger step displacements may occur and the change over from pressurization to exhaust and/or vice versa of a particular working space is provided for. Let it be assumed that the input shaft is being rotated clockwise i.e. the disc member 46 is moving leftwards in FIG. 7. Just prior to the condition illustrated in FIG. 7 the ball 41F would have been on an exhaust stroke with the passage 57F in communication through passage 56 in the flange 37 with the exhaust channel 9, it being remembered that the flange 37 is lagging to the right as the disc member 46 moves leftwards. As the disc member continues to move leftwards and the flange 37 follows, the passage 56 with which the passage 57F is in communication becomes closed by the fourth housing part 4-as the ball 41F passes through bottom dead center and subsequently the particular passage 56 comes into communication with the supply channel 8 and hence the working space behind ball 41F is pressurized. A similar procedure occurs with respect to balls 418, J, N. However, balls 41D, H, L, Q pass through top dead center whilst the particularly considered ball 41F passes through bottom dead center and, accordingly, their respective working spaces change from pressurization to exhaust.

It will be understood that the input shaft must not be allowed to lead the output shaft by more than a certain amount, in the above described form of the present embodiment, 7 1 and accordingly mechanical means, not shown, are provided for limiting to an acceptable maximum displacement of the input shaft relative to the output shaft about the position in which the position of the output shaft corresponds to that of the input shaft. Thus, the means in the present embodiment the electric stepping motor 26, controlling the input shaft may be so programmed that the limit on the lead of the input shaft is not exceeded or may be provided with a memory.

Whilst it is stated above that control of thqinput shaft 29 is performed by an electrical stepping motor, which may be of low power, it is to be understood that the input shaft 29 may be controlled in a continuous or discrete manner by any convenient means such as, for example, mechanical, hydraulic, pneumatic, electric or manual.

In FIGS. and 11 there is illustrated a second embodiment of the invention. Whilst in the first embodiment the axially directed forces imposed on members integral with or attached to the output shaft by the hydraulic pressure fluid are balanced, in the second embodiment this is not the case and means are provided for balancing a net force imposed on the members associated with the output shaft by the pressure fluid. The embodiment illustrated in FIGS. 10 and 11 comprises a housing formed of six parts 71 to 76 respectively. The housing part 71 has an internal surface a portion 77 of which conforms to a frustrum of a cone and a portion 78 at the smaller diameter end of the portion 77, which is cylindrical. A cylindrical internal cam track 79 of a ball motor is fixedly mounted in the housing part 71 at the larger diameter end of the frustoconical surface portion 77. The cam track 79 has six lobes, as may be seen in FIG. 11.

The second housing part 72 surrounds in part the first housing part 71 and bounds with the first housing part 71 an annular chamber 80.

The third housing part 73 is of annular form and is located at the end of the first housing part 71 remote from the second housing part 72 and has a radial face 81 abutting against a radial end face 82 of the first housing part 71.

The fourth housing part 74, of annular form, abuts against a radial face of the third housing part remote from the first housing part 71.

The fifth and sixth housing parts 75, 76 are concentrically rested within the third housing part 73.

An inputshaft 83 extends through a central bore 84 in the sixth housing part 76 into the chamber 85 within the housing. Disposed within the chamber 85 is a cylinder block 86, of the ball motor, which is integral with a shaft portion 87, which is a running fit within the cylindrical surface portion 78 of the housing part 71. An output shaft 88 is integral with the shaft portion 87 and the axes ofthe input shaft 83, the shaft portion 87 and the output shaft 88 are aligned and coincident with the axis of the annular sectional form of the housing parts.

Nine cylinders 89 are formed in the cylinder block 86. The axes of the cylinders are radial to the axis of the input and output shafts and are uniformly angularly disposed about the axis of the shafts 83, 88. The cylinders are open at the radially outer periphery of the cylinder block 86 and the mouths of the cylinders face the cam track 79. A ball 90 is disposed as a sliding fit within each cylinder 89.

An axially directed passage 91 extends from the bottom of each cylinder 89 to a radial surface 92 of the cylinder block facing but spaced from the third housing part 73.

Integral with the end of the input shaft 83 within the chamber 85 is a shroud 93 which includes a disc portion 94 at the outer periphery of which there is a cylindrical portion 95 in part disposed within an annular space between the cylinder block 86 and the fifth housing part 75. Atthe end of the cylindrical portion 95 remote from the disc portion 94 there is a radially outwardly directed annular portion 96 disposed within the space between the cylinder block 86 and the third housing part 73. The annular portion 96 of the shroud 93 is of a thickness in the axial direction such that its radial surfaces engage the opposed radial surfaces of the cylinder block 86 and third housing part 73 whilst permitting relative motion of the portion 96, block 86 and housing part 73 one relative to another.

The annular portion 96 of the shroud 93 has formed therein 18 axially directed passages 101 to 118 located on a circle the center of which lies on the axis of the input shaft 83 and the radius of which is the same as the radius of the circle on which lie the passages 91. The passages 101-118 are grouped in pairs. The distance between each member ofa pair of passages 101-118 is the same as the diameter of one of the passages 91 and the pairs are uniformly angularly disposed about the axis of the input shaft 83 as can be seen in FIG. 11. A passage l01a-118a extends from each passage 101-118 respectively to the radially inner cylindrical periphery of the annular shroud portion 96 which portion 96 is a sliding fit over the cylindrical, radially outer surface of the fifth housing portion 75. The passages l0la118a terminate in rectangular mouthed recesses 10117-1 18b respectively. It is arranged that the two recesses in communication with respective members of each pair of passages 101-1l8 are aligned in a direction parallel to the axis of the input shaft 83.

The sixth housing part 76 has formed in its radially outer cylindrical surface which mates with the radially inner cylindrical surface of the fifth housing part 75, four circumferentially directed channels 120, 121, 122, 123. O-ring seals 124 are provided to prevent communication between the channels 120-123 along the interface of the fifth and sixth housing parts 75, 76. The sixth housing part 76 also has formed therein two passages 125, 126 which at their ends at the outer surface of the housing are threaded for connection of hydraulic supply and return conduits. The first and third channels 120, 122 are in communication with the passage 125 and the second and fourth channels 121, 123 are in communication with the passage 126.

The fifth housing part 75 has formed therein 24 passages 154 which extend between its radially inner and outer surfaces. At their radially outer ends the 24 passages open one into each of 24 rectangular mouthed recesses 130a154a which are grouped in pairs. The members of a pair of recesses 130a154a are aligned in a direction parallel to the axis of the input shaft 83. The two members of a pair of recesses 130a154a are in communication through their associated passages and the channels l20--l23 one with each of the two passages 125, 126. Twelve of the recesses, in fact the evennumbered recesses, lie on a first circle and the odd-numbered recesses lie on a second circle. It is arranged that adjacent recesses in the two circles are in communication with different passages 125, 126. It is also arranged that adjacent recesses in the same circle are in communication with different passages 125, 126.

The disc portion 94 of the shroud 93 is provided with passages to provide communication between the opposite sides thereof.

As mentioned above, in the embodiment illustrated in FIGS. 10 and 11 the forces exerted on the cylinder block 86 by the working pressure fluid do not balance themselves and there is a resultant force, directed to the right as seen in FIG. 10. Accordingly means are provided to balance the resultant force. Such means include hydrostatic thrust bearings formed by a circumferentially extensive recess 161 in the frustoconical surface portion 77 of the first housing part 71. Oil under pressure is supplied to the recess 161 through passages 162 extending from the annular chamber 80. Further passages 163 extend from the chamber 80 to a circumferentially extensive recess 164 formed in the cylindrical surface portion 78 of the first housing part 71. Oil under pressure is introduced through a fixed restrictor into the recess 164 and an oil hydrostatic journal bearing is thereby formed. Any oil travelling rightwards, as seen in FIG. 10, along the interface between the shaft portion 87 and the first housing part 78 flows into a spillway 165 to the chamber 85 from which it can flow with any other leakage through the apertures 160 and a passage (not shown) in the sixth housing part 76 to the exterior of the servomotor. Seals 166 are provided to prevent egress of fluid along the shaft portion 87 to the exterior of the motor.

An oil hydrostatic thrust bearing opposing motion of the cylinder block 86 leftwardly as seen in FIG. 11, is formed by pressure oil supplied to an annular recess 167 in a portion of the third housing part 73 facing and engaging a radial surface of the cylinder block 86. The oil is supplied through passages 168 from a plenum chamber 169 supplied with oil through a passage which is not shown.

- With respect to the axis of the input shaft 83:

the angle subtended by a recess 130a-153a plus the angle subtended by the space between adjacent recesses 130a- 153a equals the angle subtended by half a lobe of the cam track 79, that is, in the present embodiment, 30;

the angle subtended by a recess 101b-118b plus the angle subtended by a recess 130a-153a must not be greater than the angle subtended by half a lobe of the cam track 79, (that is, in the present embodiment, not greater than 30) and may be less if the cam track 79 has dwells at the transitional points;

in the present embodiment the angle subtended by a recess 1300-1530 is I9";

the angle subtended by a space between adjacent recesses 130a153a is 11;

the angle subtended by a recess 101b118b is the same as the angle subtended by a space between adjacent recesses 1300-1530 i.e. 11;

Specific angles are mentioned above merely by way of example.

The condition of the servomotor illustrated in FIG. 11 is that when the position of the output shaft 88 corresponds to the position of the input shaft 83, if the input shaft 83 is rotated through a small angle in a clockwise direction as seen in FIG. 11, which corresponds to a rightwards displacement of the annular portion 96 of the shroud 93 as illustrated in its developed form in FIG. 12, relative to the fifth housing part 75, the following occurs.

Clockwise movement of the shroud part 96 relative to the cylinder block 86 at least partially opens the passages 91 to the odd-numbered passages 101-118 and hence to the oddnumbered passages 101a-118a and odd-numbered recesses 10112-11812, that is, the right hand circle of recesses as seen in FIG. 10.

Clockwise movement of the shroud 93 also causes movement of the recesses 101b-118b relative to the recesses 130a-153a.

The recesses in each of which is located the letter F in FIG. 12, are in pennanent communication with the passage 126 which is supplied with hydraulic fluid under pressure.

The recesses in each of which is located the letter E in FIG. 12, are in permanent communication with the passage 125 which contains low pressure hydraulic fluid returning to the drive pumps.

Considering now the balls designated 90A, 90B and 90C in FIG. 11 which are a representative group in the present embodiment which is a nine ball, six lobe arrangement, the working space in the cylinder behind the ball 90A is supplied with pressure fluid through its associated passage 91, passages 103, 1030, recesses 103b, 135a, passage 135, and passage 126. The working space behind the ball 90B is exhausting through its associated passage 91, passages 105, 105a, recesses 105b, 137a, passage 137 and passage 125. The working space behind the ball 90C is in communication though its associated passage 91 with passages 107 and 107a, recesses 107b, 1410, and passage 141 with passage 125 and is therefore exhausting. The cylinder block 86 is therefore driven in rotation in a clockwise direction. As the cylinder block 86 rotates, and assuming that the input shaft 83 and shroud 93 have been rotated through a small angle to a position at which they are stationary, the opening between passages 91 and the odd number passages 101-118 progressively decreases until finally there is no opening between the passages and when in this condition the position of the output shaft 88 corresponds to the position of the input shaft 83 and the cylinder block is hydraulically balanced in position. If, for example because of the high gain of the motor or mertia, the output shaft overshoots its position corresponding to the position of the input shaft, the resulting condition is similar to that of counterclockwise rotation of the input shaft which will shortly be described. The time during which such oscillatory hunting motion exists is a function of the motor damping and the edge-to-edge arrangement of the passages 91 with associated passages 101-118 is of great importance in this respect. g

If the input shaft and shroud are moved in a counterclockwise direction, the passages 91become opened to the even-numbered passages 102-118 and hence communication is afforded between the working spaces and respective passages 125, 126 through even-numbered passages 102a- 118a, recesses 102b-1l8b and, as seen in FIG. 12, appropriate ones of the even-numbered passages 130-152 and recesses 130a-152a. which are the left-hand circle of passages and recesses as seen in FIG. 10. However, it will be realized that a working space which is pressurized upon clockwise rotation of the input shaft from a particular position is exhausted upon counterclockwise rotation of the input shaft from the same position and a working space which is exhausted upon clockwise rotation of the input shaft from that position is pressurized upon counterclockwise rotation of the input shaft from that position.

It will be realized that if a ball passes through a top dead center or bottom dead center position whilst following the input shaft, change over from pressurization to exhaust or exhaust to pressurization, respectively, is automatically provided for by movement of the shroud plate with movement of the recesses 101b-118b relative to the recesses 130a153a. By virtue of the appropriate selection of the relative arcuate extents of the recesses 101b13 118k and 130a-153a the motor is provided with a memory whereby the input shaft 83 may lead the output shaft 88 by a certain though limited extent. Mechanical means (not shown) are provided to prevent the input shaft leading the output shaft by an amount greater than the limit imposed by the extent of the memory.

If, for example, because of hydraulic fluid leakage, the I hydraulic balance is partially lost and the output shaft becomes displaced from its position corresponding to that of the input shaft, the passages 91 become open to odd or evennumbered passages 101-118 and the cylinder block is driven back to its position corresponding to that of the input shaft at which position the passages 91 are again closed and the cylinder block is again hydraulically balanced.

It is believed that,.in particular, the description with respect to FIG. 12 makes it apparent that whilst the embodiment illustrated in and described with respect to FIGS. 10 and 11 is a rotary servomotor, a servomotor according to the present invention and similar in principle to the embodiment of FIGS. 10

and 11 may be constructed as a linear acting servomotor.

In tli fistb'f' isms 'ensaairaents'aesameaasamzm; an electrical stepping motor driving the input shaft. Such an electrical stepping motor may be comparatively cheap and lacking in power. It will be realized that the servomotor provides a very large amplification of torque. Among the uses of embodiments of the present invention may be mentioned the rotational positioning of tool carrying turrets or lathes and the control of rudders on ships.

The c555 track of the motor may be other than of general cylindrical form, with the pistons working outwardly or inwardly against the cam track, or of linear form. The cam track may be formed on a circular or part-circular path generated on a radial plane, with the pistons acting in a direction parallel to the axis of the path, i.e. normal to said plane.

Amongst the ball motors suitable for use in a servomotor in accordance with the present invention are those described in copending application Nos. 33412/64; 47458/64; 1565/65; 32862/65; 27877/66; 33231/66; 56784/66 and in U.K. Pat. Specification Nos. 924,906 and 961339.

We claim:

1. An hydraulic motor comprising an input shaft, an output shaft, a stationary member, an inlet and outlet for hydraulic fluid, a motor operable to move the output shaft relative to the stationary member, said motor comprising a plurality of pistons located one in each of a like plurality of cylinders, the pistons cooperating with a cam surface whereby when the working spaces within the cylinders behind the pistons are pressurized and exhausted in appropriate sequence the output shaft is moved relative to the stationary member, the motor being characterized by a ported device a first part of which is fixed with respect to the stationary member, a second part of which is fixed with respect to the input shaft and a third part of which is fixed with respect to the output shaft, the ported device serving to control hydraulic fluid flow between the inlet and outlet and the working spaces, the arrangement being such that when the position of the output shaft corresponds to the position of the input shaft communication between the inlet and outlet and the working spaces is prevented by the ported device, and that displacement of the input shaft and said second part of the ported device relative to the stationary member causes communication between the working spaces and the inlet and outlet to be so created that the output shaft and with it the third part of the ported device is moved by the motor to a position corresponding to the new position of the input shaft at which position communication between the working spaces and the inlet and outlet is prevented by the ported device, and that displacement of the output shaft and with it the third part of the ported device relative to the stationary member and the input shaft causes communication between the working spaces and the inlet and outlet to be so created that the output shaft is returned by the motor to a position corresponding to that of the input shaft and when so returned communication between the working spaces and the inlet and outlet is prevented by the ported device; there are two sets of passages in the third part of the ported device on opposite sides of and connecting with passages in the second part of the ported device, the passages on one side of the third part being angularly offset from the passages on the other side of the third part by a predetermined angle equal to the angle subtended at the axis of the motor by one of said passages in the second part.

2. A servomotor according to claim 1 characterized by this, that the motor is driven by an electric stepping motor, the servomotor being employed to amplify the torque of the electric stepping motor.

3. A hydraulic motor in which at least one piston reciprocates within at least one cylinder and having a stationary member, an input member and an output member, in which the output member follows the movements of the input member and having:

a. a supply of high pressure fluid;

b. an exhaust outlet;

0. first valve means controlled by relative movement of input member and output member;

d. second valve means operated by relative movement of output member and stationary member to connect all each cylinder sequentially to said supply of high pressure fluid and to said exhaust outlet;

e. first conduits connecting each cylinder to said first valve means;

f. second conduits connecting said first valve means to said second valve means; and

g. third conduits connecting said second valve means to said supply of high pressure fluid and to said exhaust outlet.

4. A hydraulic motor according to claim 3, having:

a. each cylinder carried by the output member, and

b. a cooperating cam track, carried by the stationary member, the driving force of the motor being obtained from the reaction of each piston against this track.

5. A hydraulic motor according to claim 3, in which:

a. said second conduits comprise a first and a second set of conduits, and

b. said first valve means is operated by relative movement of said input and output members to connect said first condutts to one only of said first and second sets, according to the sense of displacement between said input and out put members.

6. A hydraulic motor according to claim 4 in which:

a. the output member rotates; and

b. the cam track is of the multilobe type, so that each piston reciprocates more than once per revolution of the output member.

7. An hydraulic motor comprising an input shaft, an output shaft, a stationary member, an inlet and outlet for hydraulic fluid, a motor operable to move the output shaft relative to the stationary member, said motor comprising a plurality of pistons located one in each of a like plurality of cylinders, the pistons cooperating with a cam surface whereby when the working spaces within the cylinders behind the pistons are pressurized and exhausted in appropriate sequence the output shaft is moved relative to the stationary member, the motor being characterized by a ported device a first part of which is fixed with respect to the stationary member, a second part of which is fixed with respect to the input shaft and a third part of which is fixed with respect to the output shaft, the ported device serving to control hydraulic fluid flow between the inlet and outlet and the working spaces, the arrangement being such that when the position of the output shaft corresponds to the position of the input shaft communication between the inlet and outlet and the working spaces is prevented by the ported device, and that displacement of the input shaft and said second part of the ported device relative to the stationary member causes communication between the working spaces and the inlet and outlet to be so created that the output shaft and with it the third part of the ported device is moved by the motor to a position corresponding to the new position of the input shaft at which position communication between the working spaces and the inlet and outlet is prevented by the ported device, and that displacement of the output shaft and with it the third part of the ported device relative to the stationary member and the input shaft causes communication between the working spaces and the inlet and outlet to be so created that the output shaft is returned by the motor to a position corresponding to that of the input shaft and when so returned communication between the working spaces and the inlet and outlet is prevented by the ported device; there are two sets of passages in the third part of the ported device on opposite sides of and connecting with passages in the second part of the ported device, the passages on one side of the third part being angularly offset from the passages on the other side of the third part by a predetermined angle different from the angle subtended at the axis of the motor by a predetermined angle, whereby the axes of adjacent passages are out of alignment by a predetermined amount.

8. The hydraulic motor of claim 1 wherein said pistons are all ball-shaped.

9. The hydraulic motor of claim 1 wherein said output shaft executes linear movement.

10. The hydraulic motor of claim 1 wherein said output shaft rotates. 

1. An hydraulic motor comprising an input shaft, an output shaft, a stationary member, an inlet and outlet for hydraulic fluid, a motor operable to move the output shaft relative to the stationary member, said motor comprising a plurality of pistons located one in each of a like plurality of cylinders, the pistons cooperating with a cam surface whereby when the working spaces within the cylinders behind the pistons are pressurized and exhausted in appropriate sequence the output shaft is moved relative to the stationary member, the motor being characterized by a ported device a first part of which is fixed with respect to the stationary member, a second part of which is fixed with respect to the input shaft and a third part of which is fixed with respect to the output shaft, the ported device serving to control hydraulic fluid flow between the inlet and outlet and the working spaces, the arrangement being such that when the position of the output shaft corresponds to the position of the input shaft communication between the inlet and outlet and the working spaces is prevented by the ported device, and that displacement of the input shaft and said second part of the ported device relative to the stationary member causes communication between the working spaces and the inlet and outlet to be so created that the output shaft and with it the third part of the ported device is moved by the motor to a position corresponding to the new position of the input shaft at which position communication between the working spaces and the inlet and outlet is prevented by the ported device, and that displacement of the output shaft and with it the third part of the ported device relative to the stationary member and the input shaft causes communication between the working spaces and the inlet and outlet to be so created that the output shaft is returned by the motor to a position corresponding to that of the input shaft and when so returned communication between the working spaces and the inlet and outlet is prevented by the ported device; there are two sets of passages in the third part of the ported device on opposite sides of and connecting with passages in the second part of the ported device, the passages on one side of the third part being angularly offset from the passages on the other side of the third part by a predetermined angle equal to the angle subtended at the axis of the motor by one of said passages in the second part.
 2. A servomotor according to claim 1 characterized by this, that the motor is driven by an electric stepping motor, the servomotor being employed to amplify the torque of the electric stepping motor.
 3. A hydraulic motor in which at least one piston reciprocates within at least one cylinder and having a stationary member, an input member and an output member, in which the output member follows the movements of the input member and having: a. a supply of high pressure fluid; b. an exhaust outlet; c. first valve means controlled by relative movement of input member and output member; d. second valve means operated by relative movement of output member and stationary member to connect all each cylinder sequentially to said supply of high pressure fluid and to said exhaust outlet; e. first conduits connecting each cylinder to said first valve means; f. second conduits connecting said first valve means to said second valve means; and g. third conduits connecting said second valve means to said supply of high pressure fluid and to said exhaust outlet.
 4. A hydraulic motor according to claim 3, having: a. each cylinder carried by the output member, and b. a cooperating cam track, carried by the stationary member, the driving force of the motor being obtained from the reaction of each piston against this track.
 5. A hydraulic motor according to claim 3, in which: a. said second conduits comprise a first and a second set of conduits, and b. said first valve means is operated by relative movement of Said input and output members to connect said first conduits to one only of said first and second sets, according to the sense of displacement between said input and output members.
 6. A hydraulic motor according to claim 4 in which: a. the output member rotates; and b. the cam track is of the multilobe type, so that each piston reciprocates more than once per revolution of the output member.
 7. An hydraulic motor comprising an input shaft, an output shaft, a stationary member, an inlet and outlet for hydraulic fluid, a motor operable to move the output shaft relative to the stationary member, said motor comprising a plurality of pistons located one in each of a like plurality of cylinders, the pistons cooperating with a cam surface whereby when the working spaces within the cylinders behind the pistons are pressurized and exhausted in appropriate sequence the output shaft is moved relative to the stationary member, the motor being characterized by a ported device a first part of which is fixed with respect to the stationary member, a second part of which is fixed with respect to the input shaft and a third part of which is fixed with respect to the output shaft, the ported device serving to control hydraulic fluid flow between the inlet and outlet and the working spaces, the arrangement being such that when the position of the output shaft corresponds to the position of the input shaft communication between the inlet and outlet and the working spaces is prevented by the ported device, and that displacement of the input shaft and said second part of the ported device relative to the stationary member causes communication between the working spaces and the inlet and outlet to be so created that the output shaft and with it the third part of the ported device is moved by the motor to a position corresponding to the new position of the input shaft at which position communication between the working spaces and the inlet and outlet is prevented by the ported device, and that displacement of the output shaft and with it the third part of the ported device relative to the stationary member and the input shaft causes communication between the working spaces and the inlet and outlet to be so created that the output shaft is returned by the motor to a position corresponding to that of the input shaft and when so returned communication between the working spaces and the inlet and outlet is prevented by the ported device; there are two sets of passages in the third part of the ported device on opposite sides of and connecting with passages in the second part of the ported device, the passages on one side of the third part being angularly offset from the passages on the other side of the third part by a predetermined angle different from the angle subtended at the axis of the motor by a predetermined angle, whereby the axes of adjacent passages are out of alignment by a predetermined amount.
 8. The hydraulic motor of claim 1 wherein said pistons are all ball-shaped.
 9. The hydraulic motor of claim 1 wherein said output shaft executes linear movement.
 10. The hydraulic motor of claim 1 wherein said output shaft rotates. 